1. Field of the Invention
The present invention relates generally to transmissions, and more particularly to a variable speed friction drive unit for riding lawn mowers and the like.
2. Discussion of the Prior Art
It is known to provide a lawn mower having two drive wheels, with an independent transmission and speed control for each drive wheel. In these known constructions, a variable speed transmission serves as the clutch, differential, and means for braking. In addition, two hand levers are provided for independently controlling the drive wheels. Such a known construction eliminates the need for a steering wheel, clutch pedal or gearshift, simplifying operation of the mower while increasing maneuverability.
An example of such a mower construction is shown in U.S. Pat. No. 4,625,586, assigned of record to the assignee of the present application. The disclosure of the '586 patent is hereby incorporated in this application by express reference.
In the '586 patent, a drive unit is described which includes a pair of driving cones on a powered input shaft, and a pair of driven drums on separate output shafts mounted on independent subframes or carriages. The carriages are rockable in a frame such that each drum can engage the cone for power transmission to the corresponding drive wheel at a speed ratio dependent on the point of contact of the drum on the cone. A resilient rod connected between each carriage and the frame urges the drum toward the neutral, disengaged positions, and these rods cause the drums to contact the drive cones with sufficient force to provide torque for operation of the machine.
Although the resilient rods provide satisfactory operation of the drive unit, it would be desirable to improve the responsiveness of the unit to actuation of the hand levers, and to provide greater driving torque to the wheels without requiring the operator to substantially increase operating pressure on the hand levers. By enabling this type of adjustment of the unit, it is possible to insure that the transmission engages immediately upon actuation of the hand levers, and delivers an initial driving force of a magnitude sufficient to start the mower moving smoothly.